Implement secretbox handlers and align gacha behavior

- Add secretbox API schemas, handlers, and routes for all/showDetail/pon/multi
- Load secretbox server data through the shared serverdata loader
- Fix rarity mapping and pool rules for SR/SSR/UR special boxes
- Implement thanks festival pool behavior, including UR guarantee and SSR/UR-only rates
- Correct animation-related fields such as is_hit and lowest_rarity, and add rare UR promotion animation

Signed-off-by: Sean Du <do4suki@gmail.com>

internal/handler/api/secretbox/secretbox.go

@@ -0,0 +1,15 @@
+package secretbox
+
+import (
+	"fmt"
+)
+
+func SecretBoxApi(action string) (res any, err error) {
+	switch action {
+	case "all":
+		res, err = all()
+	default:
+		err = fmt.Errorf("unimplemented action: secretbox: %s", action)
+	}
+	return res, err
+}